For some high-speed electronic devices (also referred to here as “host devices”), it is desirable to use fiber optic cabling for interconnecting the ports of such devices. Examples of host devices include switches, routers, gateways, access points, server computers, end-user computers, appliance computers (such as network-attached storage (NAS) devices), and nodes of a storage area network (SAN). Typically, using fiber optic cabling with such a host device requires the use of active optical components (for example, to perform electrical-to-optical (E/O) and optical-to-electrical (O/E) conversions necessary for signals to be sent and received by the host device over the passive fiber optic cabling).
However, in some cases, manufacturers of the host devices do not wish to include the active optical components in the host device itself. In these cases, the host devices are designed to be used with active optical cables. An active optical cable includes, in addition to the passive fiber optic cabling, the active optical components that perform the E/O and O/E conversions necessary for signals to be sent and received by the host device over the passive fiber optic cabling. Traditionally, each active optical cable comprises a matched pair of active optical modules that are designed to be used with a single segment of fiber optic cabling (typically a duplex segment comprising two optical fibers). In one type of single-segment active optical cable, each of the matched pair of active optical modules is permanently attached to the single segment of fiber optic cabling. In another type of single segment active optical cable, each of the matched pair of active optical modules includes an appropriate connector or (other mechanism) to removably attach the single segment of fiber optical cabling to the module. With this second type of active optical cable, the fiber optic cabling used in the active optical cable can be changed (for example, to change between single mode fiber and multi-mode fiber or to replace defective cabling). However, with both types of active optical cables, the active optical modules are designed to be used with a single segment of fiber optic cabling, and the modules are designed to be together as a pair.
Each active optical module typically includes an optical transceiver, a controller, a storage device, and an electrical connector. The electrical connector is connected to a port of a host device. Typically, the host device and the active optical module exchange “transmit” and “receive” signals in electrical form (typically, as respective differential signal pairs). The optical transceiver in the active optical module handles the E/O and 0/E conversions necessary for the electrical transmit and receive signals. The interface implemented between the electrical connector and the port of the host device also includes appropriate power and ground lines for providing power and ground to the active components in the active optical module.
Manufacturers of some host devices require that, when an active optical cable is used to connect a port of a first host device to a port of a second host device, the active optical cable must first be authenticated before those ports can be enabled for use with that active optical cable. These ports are also referred to here as “authenticated” ports. This authentication is done, for example, to ensure that only active optical cables manufactured by an authorized manufacturer are used with the host devices.
The interface implemented between the authenticated ports of the host devices and the electrical connectors included in the active optical modules includes one or more signal lines over which data can be exchanged between a given host device and an active optical module that is connected to one of its authenticated ports. These lines are also referred to here as the “control interface.” In one example, when an active optical module is connected to an authenticated port of a host device, the host device uses the control interface to write challenge data to the storage device included in the active optical module. The controller in the active optical module then generates an encrypted response by encrypting the challenge data with a private key that is stored in the active optical module. The generated response data is stored in the storage device. The host device then uses the control interface to read the response data from the storage device along with a cable identifier (using the control interface that is provided between the port and the electrical connector). The challenge data, cable identifier, and encrypted response data are provided to an authentication entity (for example, software that is a part of a network management system) for authenticating the active optical module. The authentication entity uses the cable identifier to look up the private key assigned to the active optical module and then decrypts the encrypted response read from the storage device in the active optical module. If the decrypted response matches the challenge data that was encrypted, the associated active optical module is considered to be successfully authenticated.
In some applications, the active optical modules for both ends of the active optical cable must be authenticated before either of the two involved authenticated ports will be enabled for use with that active optical cable. As noted above, the active optical modules used in a single-segment active optical cable traditionally are a “matched pair” in that they are designed to always be used together as a part of the same single-segment active optical cable. For example, both of the active optical modules can be assigned the same cable or module identifier or can be assigned different module identifiers that are associated with one another a priori by the authentication entity. This is the case regardless of whether the single-segment of fiber optic cabling used with such active optical cables is permanently or removably attached to the active optical modules. As a result, it is typically not difficult for the authentication entity to determine which active optical modules are associated with one another for the purposes of authentication. This approach—where both active optical modules that are being authenticated for use with two authenticated ports—would not be suitable, however, where the two active optical modules are not a matched pair that is a part of the same single-element active optical cable.